1. Field of the Invention
The present invention relates to an exhaust gas treatment filter for an engine generator, and in particular, to a system that removes particulate matter (PM) generated by operation of a diesel engine for a generator and accumulated in a Diesel Particulate Filter (DPF) to recover the DPF.
2. Related Art
A diesel engine generates particulate matter in addition to NOx as a result of fuel combustion in nature. To prevent the particulate matter from being emitted into the atmosphere, an increasing number of diesel engines are equipped with a DPF to collect particulate matter (PM) contained in exhaust gas. This also applies to engine-driven generators.
In an engine-driven generator equipped with a DPF, a generator G is driven by a diesel engine E, electric power is supplied to a load (not shown in the drawings) through an output terminal OUT, and exhaust gas from the diesel engine E is emitted into the atmosphere through the DPF, as shown in FIG. 5.
However, the DPF is limited in terms of the amount of PM collected, and thus, once a certain amount of particulate matter is accumulated, the particulate matter needs to be removed by, for example, being burned by a certain method, to recover the DPF. For recovery of the DPF, the amount of the particulate matter and the temperature of the exhaust gas are measured and the engine E is controlled to burn the particulate matter.
That is, particulate matter amount measuring device PMD provided in the DPF measures the amount of the particulate matter, and temperature detecting device TD measures the exhaust gas temperature. Based on the results of measurements by the measuring device, an engine control unit ECU transmits and receives signals to and from the engine E to control the engine E. Thus, the particulate matter is burned in a timely manner to recover the DPF.
Furthermore, another method for recovering the DPF is to burn the particulate matter using an electric heater incorporated in the DPF (see Japanese Patent Laid-Open No. 2009-216075).
The recovery of the DPF as described above allows an engine generator using a diesel engine to be continuously operated. A failure to appropriately recover the DPF causes a large amount of particulate matter to be accumulated. This leads to a very disadvantageous situation that involves the shutdown of the generator and manual removal of the particulate matter in the DPF.
To recover the DPF, in other words, to burn the particulate matter, the exhaust gas needs to be hot above a certain temperature. In this case, what should be taken into account is that the installed engine generator typically has a capacity about three times as large as a rated input power for a load so as to be able to deal with, for example, starting of an electric motor when a large starting current flows rapidly.
Thus, in a steady state, the engine is operated under a light load, and the exhaust gas temperature remains low. Since the generator serves as a load on the engine, the engine is to be operated at a constant speed. Consequently, such method of increasing the speed in order to raise the exhaust gas temperature as is the case with automobiles cannot be adopted.
Therefore, the recovery of the DPF in the engine generator may involve a technique for burning the particulate matter using such a heater as illustrated in Japanese Patent Laid-Open No. 2009-216075.
However, providing a heater in order to burn the particulate matter is not always satisfactory from the viewpoint of fuel efficiency. Furthermore, a special DPF incorporating the heater is not preferable. Instead of the special DPF, a general-purpose DPF (for example, a DPF for automobiles) is desirably used, but adopting the general-purpose DPF for the engine generator is inappropriate as described above.
With the foregoing in view, it is an object of the present invention to provide a DPF system for an engine generator which prevents particulate matter from being accumulated without stopping power supply and which allows the DPF to be recovered in a fuel efficient manner.